HISTORY of the JEWEL BOX

PART ONE : A. 1752 — 1834

Naked-eye observations of NGC 4755 were not made in the ancient
literature or southern cultures. Although easily visible by Ptolemy
in the 2nd Century AD, no earlier reference has found. Perhaps this
is not surprising, as unlike large open clusters like the Pleiades
(M45) or Praesepe — The Beehive, or some of the bright southern
clusters; the Southern Pleiades (IC 2602), NGC 2516 in far-southern
Carina, or even M6 or M7 close to the tail of Scorpius; the Jewel Box
is fairly small.

This well-known southern cluster was first described as the “hazy star”
Kappa by Bayer in his Uranometria of 1603 AD. Later in 1752, Abbe
Lacaillé listed it in his second listing of ‘Nebulous Stars and Clusters’ and list the object as Lac-II-12 (12h
39.2m. −59°01′; January 1752) by stating ;

“5 or 6 small stars between two
of sixth magnitude.”

It was James Dunlop who made one of the first detailed drawing and
observation of NGC 4755. He listing the cluster as
Δ301 in his 629 object catalogue of
1827, stating he saw;

“(Chi Crucis, Bode)
[Herschel’s Brackets] is five stars of
the 7th magnitude, forming a triangular figure, and a star of 9th
magnitude between the second and third, with a multitude of very
small stars on the south side.”

In this paper is a drawn figure of Δ301 that Dunlop has, for some reason
made very oddly distorted. Some of the stars do differ very slightly
from how it appears today — even though Dunlop emphatically
says; “Figure 13, is a very correct
representation.” Also just as oddly
is the missing central star of the bar, which is probably one of the
most obvious features. It is also suprising that he hasn’t drawn Kappa Crucis itself as being the
brighter star, while the bright blue star at the apex of the cluster
seems too faint against the brightness of the other stars. These
differences lead some to conclude that the cluster’s appearance had undergone significant
changes ( See History of the Jewel Box Part C.
1860-1872. ), which is highly unlikely considering the slow
proper motions of stars within open clusters and what we now know
about the nature of stellar evolution over short timescales.

Also within this text is an interesting remark that, according to
Dunlop, the star is marked as “Chi” (χ) and not
the Bayer/ Bode designation ‘Kappa’ (κ).
Furthermore, this nomenclature continued until the beginning of the
20th Century, as several paper published by Francis Abbott, George
Ellery and H.C. Russell, for example, still used the Greek letter
χ or Chi.

Of course, at least in regards the unorganised state of the
ancient or medieval constellations, Crux was at one time or another
was assigned as an integral part of Centaurus. From about one
thousand years ago, many of the bright stars of both Crux and
Pointers became invisible in much of Europe by the slow effects of
precession, and these stellar assignments were generally forgotten.
This state of affairs continued into about the mid-17th Century,
until at least, when several European explorers being travelling
into the Antipodes.

Although the usage of Chi was slowly discontinued, its use had not
be properly extinguished even well after James
Dunlop’s time. Today the modern 4.5
magnitude star Chi Centauri (14h 06.0m -41°11′) is placed
some 19°N of β Centauri, which
is nearer to the north-western corner of Lupus. John Dunlop here
seems clearly wrong, making the same repeated simple error that
persisted for some time. Though in all probability it can be more
attributed to perhaps an older star atlas the Dunlop and the others
had been using. It does seem that the southern observer H.C. Russell
in the 19th Century might have become the first to correct it. In the
literature search for this whole article, he was likely the first to
refer to the cluster as Kappa Crucis in 1870. At present the lowest
ranked Greek letter currently in use within Crux
μ Crucis, which is also a wide pair
suitable for binoculars.

B. 1834 — 1899

Sir John Herschel was the next person to view this cluster, and is
giving his catalogue number HJ 3435 (or h.3435). There is
little doubt that he was very impressed with what he saw —
mainly from the copious amounts of written text on NGC 4755. During
his four-year stay in South Africa, and using his 50cm (18-inch) f/13
reflector, all observations were made from residence “Feldhausen”, which is near the
Cape of Good Hope township of Claremont. He says of the Jewel Box;

“The central star
(extremely red) and a most vivid and beautiful cluster of from 50 to
100 stars. Among the larger there are one or two evidently greenish
[stars.]; south of the red star is one 13th magnitude [Argenlander
magnitudes], also red; and near its one 12th magnitude, bluish…
The same red star taken. Several others laid down, of different
shades of green.”

This similar quote has also been duplicated in several sources.
I.e. Rev. Thomas W. Webb’s “Celestial Objects for Common Telescopes” Vol. 2, p.278 (1917).

Herschel found
the cluster very conspicuous, noting with clear admiration the great
extent of the colours. Oddly, he described many of the component
stars as “greenish”. This is immediately quite strange for an
astronomical description, as green is both hard to see and rare
— even among some of the bright and prominent
colour-contrasting double stars. I can only conclude that Herschel is
describing his overall impression of the stars rather than the
individual stars actually being greenish. It is quite possible that
Herschel is describing what he sees. Sometimes I wonder what may
cause this is more likely the speculum mirrors, which under certain
circumstances may differently absorb some wavelengths in reflecting
the light — especially when the mirror was last polished to
improve the mirrors reflectivity.

Like James Dunlop, John Herschel also made very detailed sketches
of the cluster showing some one-hundred and ten stars. Here he
says;

“Though set down by
Lacaillé as nebulous, and on that authority entered as a
nebula in Bode’s Catalogue, no nebula
is perceptible in any part of the extent of this cluster, which
though neither a large or rich one, is yet an extremely brilliant and
beautiful object when viewed through an instrument of sufficient
aperture to show distinctly very different colours of its constituent
stars, which give it the effect of a superb piece of fancy jewellery.
The area occupied by it is about 1/48th part of a square degree,
within which area have laid down, partly from micrometric measures
[from the brighter stars] and partly from inter triangulation by the
eye [for the fainter stars] the stars....”;

According to Auke Slotegraaf’s “Deepsky Observer’s Companion”, an article was published by Donald
McIntyre in the Journal of the Astronomical Society of South Africa
“An Astronomical Bi-Centenary. Abbe
de Lacaillé’s when visiting
South Africa; 1751 / 1753”; says ;

“Lacaillé
includes Kappa Crucis in his Catalogue. Sir John Herschel during his
residence at the Cape made repeated observations of his famous
cluster, but could not see any trace of nebulosity. Yet curiously,
Edward James Stone, Her Majesty’s
Astronomer at the Cape from 1870-1879, records of one of the stars
in the cluster; “Nebula: a red star
within it observed.” (Cape Catalogue
of 12,441 stars for Epoch 1880, p.316.) This red star appears to have
altered brightness since John Herschel observed it, and has been
speculated to have done so by others like Victorian amateur
astronomer Francis Abbott in 1862. The whole cluster would have
appeared nebulous to Lacaille through his tiny [12mm] …
magnifying 8×. Stone, after compiling his own catalogue, wrote;
“if is impossible, for me at least, to
the advantages which I have derived from his
[Lacaillé’s] work.”

Richard Allen, in “Star Names :
Their Lore and Meaning” (1899)
says:

“Around the 6th
magnitude is the celebrated cluster of coloured stars .... the
central and principal one being a deep red, …others green, blue
and of various shades.”

Nonetheless the colourful nature has not really impressed
everyone. An example is another quotation from Allen who quotes
(p.191) from the English astronomy author Miss Agnes M. Clerke (taken
from ‘System of the
Stars’ (1881) and
“The Herschels and Modern
Astronomy” (1895) who almost
bitterly states;

“It must be confessed
that, with moderate aperture, it fails to realise the effect of
colour implied by Sir John Herschel’s
comparison to ‘ a gorgeous piece of
fancy jewellery’. A few reddish stars
catch the eye at once; but the blues, greens and yellows belonging to
their companions are pale tints, more than half drowned in white
light.”

Allen correctly immediately puts down this comment by saying with
some abeyance; “Gould, however,
called it exquisitely beautiful.”

Still the cluster’s given name has
persisted till today, and it is possibly has become one of the most
famous quotes about any southern deep-sky object. I counted some
thirty-five sources with the same, or oddly, slightly varied wordage.
The ‘Jewel Box’ name still conjures up much to the
cluster’s mystic, and in turn, produces
much interest about the southern skies.

“This delightful
cluster, “which is estimated by Sir J.
Herschel to be composed of from 50 to 100 stars,” most of which
partake of well-marked and varied colours, forms an object that is
scarcely perceptible to the naked eye, but when under proper optical
influence it is one of the most brilliant and interesting objects in
the Southern sky. …This cluster is not only an object of
interest from the extreme beauty of colour and
arrangement…”

In most of this period the information on the cluster remained
similar and generally written for popularity among visual observers.
This probably concluded by the time of Dreyer in 1888, who published
the deep-sky New General Catalogue — scientifically
classifimg the Jewel Box among the other clusters as ‘cl, vl, stvb, kappacrucis’ — Cluster, very large, stars very
bright, surrounding Kappa Crucis.